Thermal overload relay



.Aug. 20, 1963 A. R. NOR DE NQ 3,101,397

I THERMAL OVERLOAD RELAY Filed Nov. 9,- 1960 v 5 Sheets-Sheet 1 v '65 'FIG.| Y Z3 Y 12 v 04 m INVENHR.

ALEXANDER R.NORDEN ATTORNEY Aug. '20, 1963 A. R. NORDEN 3,101,397

THERMAL OVERLOAD RELAY I Filed No v. 9, 1960 FIG. 9'

. INVENTOR.

' ALEXANDER R. NORDEN Y pflwfhwsa ATTORNEY 3 Sheets-Sheet 2 Filed Nov. .9, 19so Aug. 20, 1963 INVENTOR. ALEXANDER R. NORDEN ATTORNEY,

-A. R. NORDEN 3,101,397 I THERMAL OVERLOAD RELAY United 1 States Patent Office Federal Pacific Electric Company, a corporation of Delaware Filed Nov. 9, 1960., Ser. No. 68,233 20 Claims. cl. 200-422 This invention relates generally to an overload relay and, more particularly, roan overload relay provided with ambient temperature compensationfor electric motor control. r

One important object oft-he present invention is the provision of an overload relay for electric motor control having ambient temperature compensation in which such compensation is immune from all mechanical stresses of the contact operating mechanism at its point of operation. This arrangement represents an important desideratum since the ambient temperature compensation is isolated from the contact operating mechanism and is thus not afiected by variations resulting from extraneous mechanical stresses that. may be present in the contact operating mechanism. Pursuant to the present invention, the contact operating mechanism is of the toggle type and the ambient temperature compensating bimetal is disengaged from the toggle mechanism at the pointof overtoggling, thus renderingsuch bimetal immune from mechanical stresses in such mechanism at ov'ertoggle.

Another import-ant object of the present invention is the provision of a reset control in :an overload relay of the afor-enoted character to provide a reset time adjustment is dependent of ambient temperature variations. In this manner once the reset time is adjusted it will not be altered by ambient temperature changes. The reset time adjustment mechanism is physically displaced from, and operatively coordinated with, the ambient temperature compensating bimetal to achieve the aforenoted objectives.

Another object of the present invention is the provision of an overload relay of the aforenoted character having improved provision for selective automatic or manual reset control. 1

Yet another object of the present invention is the provision of an overload relay for motor control of the afrenoted character, which is of generally improved del the main bimetal.

I aims? Patented Aug. 20, 1963 FIG. 7 is a perspective view of the toggle mechanism with parts including the main operating bimetal and its companion operating link removed;

'FIG. 8 is a perspective view similar to FIG. 7 show: ing the complete toggle mechanism and the main operating bimetal; and

FIG. 9 is a sectional view taken on the line 99 of FIG. 1.

Referring to the drawings, and more particularly to FIGS. 1-4, there is shown an overload relay N for electric motor control having ambient temperature oom- Epfinsation. The relay 10* comprises a housing 12. which encases the operating mechanism to be described, said housing having a center body part 14 and outer cover plates 16 and 18 suitably secured to said body part. The operating mechanism comprises a main operating bimetal 29' disposed in compartment 22 defined by the insulating wall 24, said bimetal 20 being secured at one end to the leg 26 (see FIG. *8) of the mounting bracket 28 which is secured to wall 24. Extending through the leg as and bimetal 20 is a screw 30 which engages the wall 28 of bracket 28' and provides a tripping level calibration adjustment. The tree end 31 of bimetal 20 defines :a reduced width laterally oiliset actuating finger which projects through a companion slot 32. of link 34 for actuating the latter. Disposed adjacent to the bimetal 20 is a heater 396 therefor comprising a series of convolutions of wire, the terminms of which are adapted to be connected in series with the load or motor so that the bimetal will be operatively responsive to thermal overloads in the motor. An insulating plate38 is suitably secured to the heater at the side opposite to The wall 24 is slotted at 40 to slidably receive the link 34-. Mounted on the wall 24- and extending in com 7 partment 42 is a support 4 4 which mounts the operating sign and construction, economical to mass produce, ef-

ficient, reliable and foolproof in operation, and which is eminently suitable tor carrying out its intended purposes.

Other objects, features and advantages of the present invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings in the drawings:

FIG. 1 is a side elevational view of an overload relay formed in accordance with the present invention, the relay being shown with a cover plate removed and in the closed automatic reset condition;

FIG. 2 is a top view of the overload relay illustrating the selective reset control and the top portion of the reset plunger;

FIG. 3 is an enlarged sectional view taken on the line 3-3 of FIG. '1;

FIG. 4 is a view similar to FIG. 3 showing the overload relay in the manual reset tripped'position;

FIG. 5 is a fragmentary side elevational view similar to FIG. 1 showing the overload relay in the manual reset closed position;

FIG. 6 is a fragmentary view showing the position of the reset plunger and toggle mechanism in the manual I reset closed position;

member 46 and toggle link 48 at one side of the insulator plates '50 and the ambient temperature compensating bimetal 52 at the opposite side of said plates. The toggle link 48 is in the form of a narrow conductive strip having a cutout 54 adjacent the fixed end thereof to increase its sensitivity, said link carrying a contact 56 and a control'in the form of a screw 58, fabricated from insulating material, for reset time adjustment as will be described in detail hereinafter. With reference to FIGS. 7 and 8, the free end of link 48 is slotted as indicated at 60 for connection with the T-shaped end portion 62. of the U- shaped toggle spring '64. The opposite end ofthe spring 64 is slotted at 66 for the reception of the flange 68 of the operating member 46 to thereby provide an operative connection between the member 46 and said spring. The operating member 46 is in the form of an open frame having laterally spaced side members 70, the free end 72 thereof being narrowed and in operative engagement with the portion 74 of link 34. Thus the deflection of bimetal Z0 is operative to correspondingly deflect the member 4 6 through link -34 and .to actuate the toggle mechanism, as will be, described in detail. The toggle link 48 at its free end is provided with a laterally projecting finger or latch 76 for coaction with the reset plunger 78. 1

Disposed along one face of the compensating bimetal 52 is a conductive strip 79 having a contact 80 adjacent the free end of the bimetal for coaction with its companion contact 56. The compensating bimetal 52 and companion strip 79 are apertured as indicated at 82 to receive the reset time adjusting screw 58 with clearance. It will be understood that the terminals 84- and 84' are electrically connected respectively to the contacts 56 and 80 nect'ed by ,means providing lost-motion ber 46 through link 34 carrying the end 66 of the spring 64 in said direction. The opposite end of the spring 64 is restrained so that on predetermined actuation of the end 66 of the spring the latter will overtoggle and carry link 48 downwardly 'to concomitantly move contact 56 away from its companion contact 80 and open the circuit. This downward movement of link 48' will continue until the head of screw 53 carried by said link engages the bimetal 52. which servesas a limit stop for the overtoggle of the linkage. On cooling of the main bimetal 2c in accordance with the adjusted position of the screw 58 the linkage will reset to close the circuit. The terminal point of over-toggle is under the control of screw 58 which is adjustable to adjust the circuit reset time. Thus the greater the adjusted spacing between the head of screw 58 and the bimetal 52 the longer the reset time as a consequence of the longer stroke or travel required for resetting the toggle after tripping. Thus the terminal tripping point of the toggle is determined by the adjusted position of screw 58.

It will be noted that the reset time adjustment 58 is independent of ambient temperature variations so that once the reset time is adjusted it will not be altered by changes in ambient temperature. This adjustment, while physically displaced from the bimetal 52, is operatively coordinated therewith, the screw 58 cooperating with said bimetal to determine the terminal tripping point of the toggle mechanism as described above. At the dead-center pointof the toggle, the bimetal 52 is about to separate portion 52 provided with a latch portion 92' which. is operatively coupled with latch 76 of the toggle link 48 under the conditions to be described. Below the portion 99 of the plunger there is provided a laterally projecting part 94 which is slotted at 96 for the reception of the arm 98 of the control spring MP0.

The spring 1% is provided with a-cincular bearing portion 1021 which is seated on stud MM integral with the housing (see FIG. 9) and a finger portion 106 which extends outwandly of the housing through the slotted portion res thereof. Projecting into the slotted portion 1% is a detent lltl and portion 106 is selectively positionable on either side of said vdetent. To shift portion M6 to an opposite position to alter the operation of the relay said portion is manually depressed laterally to the broken line position res shown in FIG. 9' to bypass the detent 110 and pivoted about stud W4 and released to engage in such oppositeposition against the detent. It will be understood that the housing is cutaway as indicated at 112 to receive spring 100 and its companion part d4 with the requisite operating clearances. The portion 10s is laterally offset with nespe'ctto the spring 100 as best shown in FIG. 9, said spring being formed by suitably bending a length of spring wire. 1

Referring to FIGS. 1-3, the portion 106 is shown in the automatic resetiposition in which the spring arm 98 is disposed against the wall 114 or the housing and the plunger 78' is retracted inthe housing (FIG. 1). In this from toggle link 48. At that moment, the bimetal 52 is immune to all mechanical stresses within the toggle mechanism and therefore the overto-ggle point is not affected by variations in mechanical stresses present in such toggle mechanism. Referring to FIG.' -3,,on an ambient temperature rise both biinetals 2t) and 52 will deflect in the same direction, i.e., an upward direction and said bimetals are physically coordinated so that a predetermined thermal overload will govern tripping of the toggle mechanism independent of ambient temperature variations. Thus ambient temperature variations will haye no eflect on the overload tripping level as the ambient tem perature deflection of the main bimetal will be neutralized by the deflection of the compensating bimetal which governs the position or the contacts 56, 80.

It has been shown that bimetal 52 and toggle element 48 cooperate in both over-toggled configurations of the relay, that is, both when the contacts are closed and when the contacts are open. When the contacts are closed the coaction is direct in that contact 56 on toggle element 48 pressesragainst contact 80 on bimetal 48. When the contactsare open, element 48 is mechanically connected to bimetal 52 through screw 53. During the process of overtoggling, element 48 is free of constraining connection to bimeta-l 5 2, the range of free or lost motion being established by the adjusted spacing between the head or" screw 58 and birnetal 52. as mentioned above. The element 48 of the toggle and the bimetal 52, which cooperate with each other mechanically only at the ends of the range of motion of toggle element 48, are thus interconcoupling therebetween. V

The reset plunger 78 is of arcuate configuration and is preferably molded of a suitable insulating material, said plunger being slidably mounted in a complementary slot 88 of the housing 12. The slot 88 extends through thehousing at one end as indicated at 88 for the extension therethrough of the indicator portion 96 of the plunger.

The lower end of the plunger has a laterally projecting condition the latch portion 92 of the plunger is physically out of contact with latch '76 of the toggle mechanism which is free for the aforedescribed nonm al overto'ggling and resetting operation. Accordingly in the automatic reset position the plunger 78 is disposed out of operation with the toggle mechanism, which is free for automatic resetting subsequent to tripping on thermal overload, and thus exerts no control influence over such mechanism. In the opposite manual reset position of portion 166 (FIGS. 4-6) the arm '98 of the control spring biases the plunger in a direction outwardly of the housing and with the contacts and toggle mechanism closed the latch 76 or the toggle mechanism coacts with latch portion 92' to latch the plunger down, i.e. in retracted position. On tripping of the toggle mechanism on thermal overload the latch 76 releases latch portion 92' and the plunger is shifted to an extended position with respect to the housing as shown in broken lines in FIG. 5 under the influence of the aforenoted spring biasing. In this position the indicator por tion of the plunger is fully exposed to indicate thetripped condition of the relay. With reference to FIG. 4, it will be noted that in the manual reset tripped condition of the relay the portion 92 of the plunger blocks the latch 76 to block the automatic resetting of the toggle mechanism. Thus the mechanism must be manually reset which is accomplished by depressing the plunger at portion 90 slightly beyond latch 7 6 so that the latter may relatcth the plunger in the position shown in FIGS. 5 and 6 and permit the resetting of the toggle mechanism. It will be noted that in the manual reset tripped position the spring in the art, and therefore the invention should be broadly construed in accordance with its full spirit and scope.

Having thus described my invention What I claim as new and desire to secure by Letters Patent is:

1. A thermal overload relay for an electric circuit, comprising a companion pair of separable contacts, operating mechanism therefor including togle linkage and an operating device comprising a thermal element responsive to a t predetermined thermal overload to over-toggle said link age and open said contacts, and an ambient temperature compensating thermal element separate from but cooperating with said operating mechanism to control at least one over-toggle point of said linkage, said compensating element being physically separate from and separated from said operating mechanism at the instant (following overtoggle of said linkage.

2. An overload relay in accordance with claim 1 wherein one of said contacts is carried by an element of said toggle linkage and the other of said'contactsis carried by said compensating element at a point thereof that moves with variations in ambient temperature, said contacts when closed constituting one of the over-toggle control points of said linkage.

3. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal having relatively fined and movable portions, said compensating bimetal being physically displaced from said operating bimetal and operatively coordinated therewith, said compensating bimetal physically separating from said operating mechanism at the point of contact opening of said linkage, said toggle linkage comprising an operating member operatively connected to said operating bimetal, a toggle link carrying one of said contacts and a toggle spring interposed between said operating member and toggle link for biasing the latter in the contact open and closed positions'thereof, and the other contact being carried by said movable portion of said compensating bimetal, the latter restraining the movementor said linkage in the contact closed position thereof.

4. Anoverload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal having an active portion cooperable with said operating mechanism, said compensating bimetal being physically displaced from said operating bimetal, said compensating bimetal physically separating from said operating mechanism at the point of contact opening overtoggle of said linkage, said bimetals'being disposed at opposite sides of said toggle linkage and arranged to deflect in thesame direction in response to ambient temperature variations, and a heater in heat transfer relation with said operating bimetal adapted to be connected in circuit with the load.

5. A thermal overload relayhaving ambient temperature compensation, comprising a companion pair of contacts, operating mechanism therefor including toggle linkage comprising a generally U-shaped toggle spring, a cantilever operating bimetal having a heater responsive to overloads in the load circuit for actuating said toggle linkage to open and close said contacts, said toggle spring biasing said'contacts in said open and closed positions on overtoggling of said linkage, and a cantilever ambient temperature compensating bimetal disposed at the opposite side of said linkage to said operating bimetal, said cornpensating bimetal being arranged to deflect in the same direction as said operating bimetal and in physical coordination therewith in response to ambient temperature variations, saidcompensatingbimetal restraining the movement of said linkage in the contact closed position thereof and physically separating from said linkage at the point of overtoggle thereof to open said contacts.

6. A thermal overload relay having ambient temperature compensation, comprising a companion pair of contacts, operating mechanism therefor including toggle linkage comprising a generally U-shaped toggle sprin a cantilever operating bimetal having a heater responsive to overloads in the load circuit for actuating said toggle v 6 linkage to open andclose said contacts, said toggle spring biasing said contacts in said open and closed positions on overtoggling of said linkage, and a cantilever ambient temperature compensating bimetal disposed at the opposite side of said linkage to said operating bimetal, said compensating bimetal being arranged to deflect in the same direction as said operating bimetal land in physical coordination therewith in response to ambient temperature variations, said compensating bimetal restraining the movement of said linkage in the contact closed position thereof and physically separating from said linkage at the point of overtoggle thereof to open said contacts, the latter being carried by said linkage and compensating bimetal, respectively, at the only point of physical ce-ordination thereof in the contact-opening over-toggle operation of said linkage.

7. A thermal overload relay for an electric circuit, comprising a companion pair of separable contacts, operating mechanism there-for including toggle linkage and an operating member responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and ambient temperature compensating means cooperable with said operating mechanism, said means physically separating from said operating mechanism on said overtoggle of said linkage in the contact-opening direction so that said means is substantially unalfected by mechanical stress variations in said mechanism, and a reset time control for said operating mechanism independent of ambient temperature variations.

8. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal cooperating with said operating mechanism in only one of the two over-toggle conditions of the toggle linkage,

' coordinated with, said compensating bimetal whereby said reset time control is unafiected by ambient temperature variations.

9. An overload relay having ambient temperature compensation, comprising a comp-anion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to pro-determined thermal overloads to over-toggle said linkage and open said contacts, and an ambient temperature compensating bimetal spaced physically from said operating bimetal and thermally co-ordinated therewith, said ambient tempera ture compensating bimetal having lostamotion connecting means to said toggle linkage effective to control the points of over-toggling thereof both when the contacts are closed and when the contacts are open, said lost-motion connection providing a reset time control for said operating mechanism whose reset time is unaffected by ambient temperature variations.

10. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal interposed in said operating mechanism, said compensating bimetal being physically displaced from said operating bimetal and operatively coordinated therewith, and a reset time control for said operating mechanism physically displaced from, and operatively coordinated with, said compensating bimetal whereby said reset time control is unaffected by ambient temperature variations, said reset time control comprising an adjustable stop carried by said toggle linkage, said stop engaging said compensating bimetal on contact opening overtoggle of said linkage to limit the contact opening movement thereof.

11. An overload relay having ambient temperature compensation, comprising a companion pair of separable con- 7 tacts, operating mechanism therefor including toggle linkage and an operating bimetal responsivejto predetermined v bimetal, the latter restraining the movement of said linkage in the contact closed position thereof, and a reset time control for said operating mechanism comprising an adjustable stop carried .by said toggle link, said stop being physically displaced from, and operatively coordinated with, said compensating bimetal, said stop engaging said compensating bimetal on contact opening over-toggle of said linkage to determine the contact opening movement thereof. v

"12. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including to gle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal interposed in said opera-ting mechanism, said compensating bimetal being physically displaced from said opcrating bimetal and operatively coordinated therewith, said toggle linkage comprising an operating member operatively connected to said operating bimetal, a toggle link carrying one of said contacts and a toggle spring interposed between said operating member and toggle link for biasing the latter in the contact open and closed positions thereof, and the other contact being carried by said compensating bimetal, the latter restraining the movement of said linkage in the contact closed position thereof, and a reset time control for said operating mechanism comprising an adjustable stop carried by said toggle link, said stop being physically displaced from, and operatively coordinated with, said compensating bimetal, said stop engaging said compensating bimetal on contact opening overtoggle of said linkage to determine the contact opening movement thereof, said stop being constituted by an ad justable screw extending freely through an opening provided in said compensating bimetal, said screw having a head engageable with said compensating bimetal to determine the contaot'opening movement of said linkage, the clearance between said head and said compensating bimetal in the contact closed position of said linkage being adjustable to concomitantly adjust the reset time of said linkage subsequent to tripping. t

113'. An overload relay having ambient temperature compensation, comprising a companion pair of separable con tacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal interposed in said operating mechanism, said compensating bimetal being physically displaced from said operati-ng bimetal and operatively coordinated therewith,said

toggle linkage comprising an operating member operatively connetced to said operating bimetal, a toggle link carrying one of said contacts and a toggle spring interposed between said operating member and toggle link for biasing the latterin the contact open and closed positions thereof, and the other contact being carried by said compensating bimetal, the latter restraining the movement of said link- 7 age in the contact closed position thereofland a reset time control for said operating mechanism comprising an adjustable stop carried by said tog-gle link, said stop being 14. A thermal overload relay having ambient tempera:

ture compensation, comprising a companion pair of contacts, operating mechanism therefor including toggle linkage comprising a general ty U-shaped toggle spring, a cantilever operating bimetal having a heater responsive to overloads in the load circuit for actuating said toggle linkage to open and close said contacts, said toggle spring biasing said contacts in said open and closed positions on,

overtoggling of said linkage, and .a cantilever ambient temperature compensating bimetal disposed at the opposite side of said linkage to said operating bimetal, said compensating bimetal being arranged to deflect in the same direction as said operating bimetal and in physical co ordination therewith in response to ambient temperature variations, said compensating bimetal restraining the movement of said linkage in the contact closed position thereof and physically separating from said linkage at the point of overtoggle thereof to open said contacts, and a reset time control for said operating mechanism physically dis-- placed from, and operatively coordinated with, said compensating bimetal whereby said reset time control is unaffected by ambient temperature variations 15. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature compensating bimetal interposed in said operating mechanism, said compensating bimetal being physically displaced frornsaid operating bimetal andoperatively coordinated therewith, said toggle linkage comprising an operating member operatively connected to said operating bimetal, a toggl'e'link carrying one of said contacts and a toggle spring interposed between said operating member and toggle link for biasing the latter inthe contact open and closed positions thereof, and the other contact being carried by said compensating bimetal, the latterrestraining the movement of said linkage in the contact closed position thereof, and a reset time control for said operating mechanism comprising an adjustable stop carried by said toggle link, said stop beingphysically displaced from, and operatively coordinated with, said compensating bimetal, said stop engaging said compensating bimetal on contact opening over-toggle of said linkage to determine the contact opening movement thereof, and control means selectively providing for automatic or manual resetting of said linkage subsequent to overtoggling.

16. An overload relay having ambient temperature compensation, comprising a companion pair of separable contacts, operating mechanism therefor including toggle linkage and an operating bimetal responsive to predetermined thermal overloads to overtoggle said linkage and open said contacts, and an ambient temperature com-- pensating bimetal cooperable with said operating mechanism, said compensating bimetal being physically displaced from said operating bimetal and operatively coordinated therewith, said compensating bimetal physicaltively coupled therewith for selecting the operation thereof, said plunger being operatively uncoupled from said linkage in the automatic reset position of said control member and being operatively connected to said linkage in the manual reset position of said control member, said plunger in said latter position of said control member blocking the resetting of said linkage subsequent to overplaced from said operating bimetal and operatively co-' ordinated therewith, said compensating bimetal physically separating from said operating mechanism at the point of overtoggle of said linkage, a reset control member selectively movable to automatic and man-ual reset-positions, a reset plunger operatively connected to said control member for control thereby, said plunger and linkage having cooperating pants in latching engagement restrain- 7 ing said plunger in position in contact closed position of said linkage with said control member in said manual reset position, said plunger in said last mentioned position being biased into engagement With said linkage, the overtoggling thereof releasing said plunger under said biasing influence for movement to a tripped position in which said plunger blocks the resetting of said linkage, said plunger having an indicator portion at its outer end indicating the tripped condition of said linkage, said portion being manual-1y depressible to clear said cooperating parts thereby permitting the resetting of said linkage and the relatch of said cooperating parts.

"1 8. A thenmal relay having an adjustable tripping point and ambient temperature compensation and having an adjustable reset time independent of mripping point adjustment and ambient temperature variations, said relay including an active bimetal, load-current carrying means causing heating of said active bimetal in response to,

load current, and ambient temperature compensating bimetal, companion contacts, and anover-centering snapacting device rfior opening and closing said contacts under control of said bimetals, both of said bimetals being mechanically coupled to said snap-acting device and being effective to control snap-action thereof both in the contact-opening direction and in the contactclosing direction, said active bimetal having an adjustment eifective to control the current-level at which automatic opening of the contacts occurs, the mechanical coupling of one of bimetals including a positive coupling to said snap-acting device eifective only'when said device is in its closed condition. and including a positive coupling to said device elfective onlywhen said snapacting device is in its iopen condition, said snap-acting device having a range of motion during its over-centering operation when it is free of restraint by both of said positive-acting coupling means, and means for adjusting, the range of restraint-free operation of said device, for thereby controlling the reset time following an automatic contact opening operation, reclosing of the contacts occurring automatically at the end of the reset time.

19. A thermal relay having an adjustable tripping point and ambient temperature compensation and having an adjustable reset time independent of tripping-point adjustment and ambient temperature variations, said relay including an active bimetal, load-current carrying means causing heating of said active bimetal in response to load current, an-ambient temperature compensating bimetal, companion contacts, and an over-centering snapacting device for opening andclosing said contacts under control of said bimetals, both of said bimetals being mechanically coupled to said snap-acting device and being efiective to control snap-action thereof both in the contact-opening direction and in the contact-closing direction, said active bimet-al having an adjustment effective to control the current-level all which automatic opening of the contracts occurs, the mechanical coupling of said oompensating bimetal to said snap-acting device including means constraining said snap-acting device in the closed condition of the device and means constraining said -device in the open condition of said device, and said snapacting device having a range of motion during the snap action thereof when the device is free of constraint by both of said constraining means, one of said constraining means being adjustable for thereby controlling the reset time following an automatic over-centering operation in i one direction, reverse operation of the contacts occurring automatically at the end of an adjustable reset time. p

20. A thermal relay having an adjustable tripping point and ambient temperature compensation and having an adustable reset timeindependent of tripping-point adjustment and ambient temperature variations, said relay including an active bimetal, load-current carrying means causing heating of said active bimetal in response to load current, an ambient temperature compensating bimetal, companion contacts, and an over-centering snapacting device for opening 'and closing said contacts under control of said bimetals, both of said bimetals being mechanically coupled tosaid snap-acting device and being effective to control snap-action thereof both in the contact-opening direction and in the contact-closing direction, said active bimetal having an adjustment effective to control the current-level at which automatic opening of the contacts occurs, and said compensating bimetal having means providing mechanical coaction with said snap-acting devices only at the ends of a range of free and unconstrained relative motion between the compensating bimetal and the snapaacting device, said last named means including a device for adjusting said range of free motion for thereby controlling the reset time following an automatic contact-opening operation, reclosing of the contacts-occurring automatically at the end of the reset time.

References Cited in the file of this patent UNITED STATES PATENTS 2,599,473 Miller June 3, 1952 2,658,975 Zuckerman Nov. 10, 1953 2,691,082 Turner et a1 Oct. 5, 1954 2,840,664. Anderson et al June 24, 1958 2,851,556 Van Valkenburg Sept. 9, 1958 2,908,786 Schleicher Oct. 13, 1959 2,942,081 Ramsey et a1 June 21, 1960 

1. A THERMAL OVERLOAD RELAY FOR AN ELECTRIC CIRCUIT, COMPRISING A COMPANION PAIR OF SEPARABLE CONTACTS, OPERATING MECHANISM THEREFOR INCLUDING TOGLE LINKAGE ANS AN OPERATING DEVICE COMPRISING A THERMAL ELEMENT RESPONSIVE TO A PREDETERMINED THEREMAL OVERLOAD TO OVER-TOGGLE SAID LINKAGE AND OPEN SAID CONTACTS, AND AN AMBIENT TEMPERATURE COMPENSATING THERMAL ELEMENT SEPARATE FROM BUT COOPERATING WITH SAID OPERATINGH MECHANISM TO CONTROL AT LEAST ONE OVER-TOGGLE POINT OF SAID LINKAGE, SAID COMPENSATING ELEMENT BEING PHYSICALLY SEPARATE FROM AND SEPARATED FROM SAID OPERATING MECHANISM AT THE INSTANT FOLLOWING OVERTOGGLE OF SAID LINKAGE. 